What are the standards and features of these wind-breaking and spoiler boards?

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3.jpg Wind breaking ring The wind breaking ring is a component on the chimney. In order to avoid or reduce the Karman vortex generated by the air flow and cause the chimney to resonate, a spiral winding band or fin is welded to the uppermost section of the chimney. There are also axial arrangements. (Slender tall towers also often have this structure. ) When fluid flows transversely through a cylinder, vortices are alternately generated on both sides of the back of the cylinder, and a vortex wake is formed after separation (Figure 4-8). Also known as "Karman's vortex". The reason for the generation of vortices is the mutual conversion of kinetic energy and pressure energy after the fluid is blocked, and the pressure changes along the circumference of the cylinder and the thickness direction of the boundary layer. The greater pressure of the fluid outside the boundary layer forces the particles with smaller pressure inside the boundary layer to flow in the opposite direction, thus thickening the boundary layer, forming a vortex, and then detaching from the surface of the cylinder. The vortex is elongated and disappears as the flow speed increases. When the vortex on one side grows up and breaks away, the vortex on the other side is forming and growing up, thus forming two rows of vortex wakes alternately, which looks like a "vortex street". The vortices in the Karman vortex street are generated, detached, and dissipated at a certain frequency. The pressure on both sides of the cylinder also changes periodically at the same frequency. When the vortex shedding frequency is equal to the natural vibration frequency of a certain mode of the cylinder, the cylinder will vibrate violently. This phenomenon is an induced vibration. According to experiments, the vortex shedding frequency is related to the outer diameter of the cylinder and the fluid velocity. The tower equipment is affected by wind load and the lateral flow of fluid in the shell side of the shell-and-tube heat exchanger. When the above conditions are met, periodic vortices will also appear and induce vibration. In severe cases, it will lead to equipment failure and damage. The chimney design should avoid resonances caused by eddy currents. Increasing the stiffness of the chimney or adding a layer of concrete lining can improve the chimney's ability to withstand vibrations. But the most effective way is to weld a spiral outer "wind-breaking ring" on the uppermost section of the chimney. The setting of the wind-breaking circle should comply with the following regulations: a. Setting conditions: When the critical wind speed of the chimney is less than 6~7m/s, the wind-breaking circle should be set. When the critical wind speed of the chimney is 7~13.4m/s and is less than the design wind speed, and it is not economical to change the chimney height, diameter, increase thickness and other measures, a wind breaking circle can also be set up. b The chimney shape coefficient for setting the wind breaking circle range should be selected according to the surface roughness. c Setting location: When the wind breaking circle needs to be set, it should be set within a range of not less than 1/3 of the height of the chimney from the upper end of the chimney. d Type and size of the wind breaking circle: a) Staggered upright plate type: the thickness of the upright plate is not less than 6mm, the length is not more than 1.5m, and the width is 1/10 of the outer diameter of the chimney: the number of vertical plates in each circle is 4, evenly distributed along the circumference of the chimney, and adjacent circles of vertical plates are staggered 45° from each other. b) Spiral plate type: The thickness of the spiral plate is not less than 6mm, and the plate width is 1/10 of the outer diameter of the chimney. There are three spiral plates, evenly distributed along the circumference, and the spiral pitch can be 5 times the outer diameter of the chimney.